The present invention relates to closures for containers having an externally screw threaded neck and more particularly to such closures which are formed with a tamper evident band.
Manufacturers of foodstuffs, beverages, medicaments, dentifrice and the like are concerned to ensure that products they place on the market are not tampered with before being opened by the ultimate consumer of the goods. For this purpose it has become conventional to include in closures for such goods means which will indicate whether the closure has been tampered with before purchase. In the case of containers having an externally screw threaded neck it is common to provide the closure with a tamper evident band which engages behind a retaining flange formed on the neck of the container. The tamper evident band is joined to a depending skirt forming part of the closure by a number of frangible bridges. On application of the closure to the container the band is forced over the retaining flange, however, when the closure is unscrewed from the container the bridges are sheared as the band is trapped behind the retaining flange while the closure moves up the neck of the container.
While such tamper evident bands have been widely accepted there is a delicate balance between the two conflicting requirements. On the one hand, one must be able to apply the closures to containers at very high speed without inadvertently breaking the bridges, or breaking or deforming the band itself, or deleteriously affecting the seal between the closure and the container. On the other hand, the band must be sufficiently tightly secured behind the retaining flange and the bridges and/or the band must be sufficiently easily broken that the closure cannot be removed from the container without rupturing the bridges and/or the band.
Another problem is that-an unauthorized person might attempt to remove the closure and tamper evident band, without damaging the band or frangible bridges, in order to contaminate or replace the container contents and then reapply the closure. Such operation might be attempted with the assistance of a thin device, such as a knife blade, wedged up between the tamper evident band and the neck of the container to which the closure has been applied. The devices might then be levered outwardly in order to expand the inner diameter of the band so that it may be passed back over the retaining flange of the container. In such a process the device will be edged around the circumference of the band so as to gradually ease the band over the retaining flange at a continuously lengthening portion of the band circumference.
Closures of the type mentioned above are used around the world in extremely large numbers. To be commercially acceptable such closures must be capable of being produced very rapidly in automated machinery. This itself may produce a conflict with the functionality of the closure and/or its tamper evident band.
The arrangement according to the present invention is designed to provide the public with an alternative form of closure having a tamper evident band.
The present invention in its broadest aspect consists in a closure for a container having an externally screw threaded neck, the closure comprising a top portion and a depending skirt which has on its internal surface a complementary screw thread, a free edge of the depending skirt being joined by a plurality of frangible bridges to a tamper evident band, the band comprising a generally cylindrical body portion and a segmented rib extending inwardly of the body portion and adapted to provide a lip to engage under a retaining flange extending outwardly from the neck of the container below the screw thread thereon, the rib having an upper side facing generally towards the top of the closure and an under side facing generally away from the top, the body portion being provided with projections or other localised areas of thickening to enhance the longitudinal stiffness of the body portion while still permitting it to expand radially as it is forced over the retaining flange on a container.
In a first preferred aspect the present invention consists in a closure for a container having an externally screw threaded neck, the closure comprising a top and a depending skirt which has on its internal surface a complementary screw thread, a free edge of the depending skirt being joined by a plurality of frangible bridges to a tamper evident band, the band comprising a generally cylindrical body portion and a continuous or segmented rib extending inwardly of the body portion and adapted to provide a lip to engage under a retaining flange extending outwardly from the neck of the container below the screw thread thereon, the rib having an upper side facing generally towards the top of the closure and an under side facing generally away from the top, the closure being characterized in that the upper side of the rib comprises a first surface contiguous with the body portion of the band, which surface slopes inwardly and downwardly from the top, and a second surface which is positioned radially inwardly from the first surface, the second surface having a slope angle more nearly normal to the longitudinal axis of the closure than the first surface is to that longitudinal axis.
In the prior art closures the upper side of the rib has always been linear in cross-section. The upper side has either lain in a plane normal to the longitudinal axis of the closure or it has been a simple frusto-conical surface inclined to that axis. In the former case it has been difficult to mold as the planar surface is normal to the direction in which the core of the mold must be withdrawn from the cap. In the latter case there is more likelihood of the rib being able to be forced upwardly over the flange on the container neck. The present invention has resolved these problems by providing the upper side of the rib with a compound surface having a more steeply angled radially outer surface which assists molding of the rib and, preferably, a substantially planar radially inner surface which increases the difficulty of removing the closure intact from a container. There is preferably a relatively clearly defined junction between the first and second surfaces on the upper side of the rib. However, they may merge together gradually such that the upper side of the rib is generally arcuate in cross-section. It has been found that improved resistance to removal of the closure from the container can be obtained in this way while facilitating the molding of the closure. This latter aspect is important as for economic reasons, it is necessary that the closures and their associated tamper evident bands must be capable of being molded at extremely high rates.
The first surface on the upper side of the rib preferably comprises from 25% to 75% and more preferably 45% to 55%, of the radial width of the upper side of the rib. The first surface preferably has a slope angle to a plane normal to the longitudinal axis of the closure of from 10xc2x0 to 60xc2x0, more preferably 12xc2x0 to 40xc2x0 and most preferably 15xc2x0 to 25xc2x0. The second surface on the upper side of the rib preferably comprises from 75% to 25% and more preferably 55% to 45% of the radial width of the upper side of the rib. The second surface preferably lies in a plane normal to the longitudinal axis of the closure or at an angle of up to 10xc2x0 to that plane, most preferably it lies in that plane.
In carrying out the present invention it has been found that during the injection moulding of closures from an injection mould which defines a rib having an upper side comprising a first annular surface and a second annular surface the clear distinction between the first and second surfaces may be lost, or at least difficult to discern, in the moulded product. It is thought that this may be due to the second annular surface being distorted and dragged into a slope angle similar to that of the first surface as the closure is ejected from the mould. Despite the anomaly that the mould clearly displays the two surfaces but the moulded closure does not, it has been found that the closures moulded from such a mould show superior resistance to being tampered with as compared to similar closures moulded in a mould not defining the upper side of the rib as having first and second surfaces.
Therefore in another aspect the present invention consists in a closure for a container having an externally screw threaded neck, the closure comprising a top and a depending skirt which has on its external surface a complimentary screw thread, a free edge of the depending skirt being joined by a plurality of frangible bridges to a tamper evident band, the band comprising a generally cylindrical body portion and a continuous or segmented rib extending inwardly of the body portion and adapted to provide a lip to engage under a retaining flange extending outwardly from the neck of the container below the screw thread thereon, the rib having an upper side facing generally towards the top of the closure and an under side facing generally away from the top, the closure being characterised in that the closure is formed by injection moulding from a synthetic plastics material in a mould which defines the upper side of the rib as comprising a first surface contiguous with the body portion of the band, which surface slopes inwardly and downwardly from the top, and a second surface which is positioned radially inwardly from the first surface, the second surface having a slope angle more nearly normal to the longitudinal axis of the closure than the first surface is to that longitudinal axis. The mould surface preferably has the other characteristics previously described as being preferred for the upper side of the rib itself.
In another embodiment of the invention the radially inner surface of the band is provided with an array of radially spaced apart inwardly extending projections positioned between the rib and a free edge of the band. The projections, or some of them, may, if desired, make contact with the under side of the rib across the longitudinal width of the band or they may stop short of the lower free edge of the band. They preferably are aligned parallel with the longitudinal axis of the closure but may be inclined to that axis. These inwardly extending projections make it difficult for a person deliberately trying to expand the diameter of the band and to ease it off the neck of the container intact by inserting a blade or other tool between the band and the container.
In a particularly preferred arrangement, the rib is segmented and alternate ones of the projections are spaced below the gaps between adjacent segments and are not connected to the rib. The remaining projections preferably abut at the upper ends with respective ones of the segments. These remaining projections preferably abut the segments at their respective mid-points. The projections are preferably inclined radially inwardly as they approach the rib, however they preferably do not extend inwardly from the radially inner surface of the body portion of the band as far as the rib does. The rib preferably extends inwardly beyond the projection by a distance substantially equal to the width of the second surface on the upper side of the rib.
The rib formed to engage with the retaining flange on the container may be continuous or segmented about the band, however if it is segmented it will still extend about a majority of the circumferential extent of the inside surface of-the band. The rib segments, when present, are preferably evenly spaced about the inside circumference of the band and occupy at least 50%, preferably at least 65% and most preferably at least 80%, of the internal circumference of the band. The rib preferably has a sufficiently broad base where it joins the body portion of the band that the rib is resistant to flexing upwardly as it is forced past the retaining flange during application of the closure to a container.
Each of the rib segments is preferably formed with two substantially planar end surfaces which are inclined to the axis of the closure and face away from the closure top, i.e., they face in a direction that a mould core used to mould the closure was withdrawn. The planar end surfaces are also preferably inclined to a notional radial plane extending from the longitudinal axis of the closure to the end of the respective rib segment such that the ends are inclined to the skirt of the closure by an included angle that is less than the included angle that the respective notional plane makes with the skirt.
The tamper evident band is further preferably provided with areas of localised thickening which extend outwardly from an external surface of the body portion of the band. The areas of thickening further preferably extend parallel to the longitudinal axis of the closure and across the longitudinal width of the band.
The areas of outer thickening serve to reinforce and strengthen the tamper evident band. The reinforcement of the band preferably enhances the vertical stiffness of the band whilst retaining a sufficient flexibility to facilitate application of the closure to the container. The reinforcement also allows sufficient axial force to be applied to the free end of the band in order to successfully eject the closure from a core portion of a mould used in the closure production. The reinforcement of the band further reduces the possibility of the closure being tampered with and the band stretched in order that it may be eased back over the retaining flange on a container to which the closure has been applied.
The bridges are preferably evenly spaced about the circumference of the closure but may be optionally arranged in two groups which are diametrically opposed to one another. Each group may preferably occupy from one quarter to one third of the circumference of the closure while each of the spaces between the groups occupies from one quarter to one sixth of that circumference. Each group of bridges is preferably made up of from 4 to 10 bridges equally spaced apart within the group.
The individual bridges in each group may have an axis parallel to the axis of the closure. Preferably, however, the axis of each bridge is inclined to the axis of the closure, more preferably it is inclined such that when seen in side elevation the upper end of the bridge is inclined to the left relative to its lower end. This particularly preferred arrangement is predicated by the fact that most screw threads tighten in a clockwise direction. The preferred inclination of the bridges allows them to bend as the closure is screwed onto a container. This stabilizes the band and reduces the likelihood of it, or the bridges, breaking or distorting during application. Conversely this preferred inclination of the bridges means that as the closure is unscrewed the bridges are straightened out and this serves to concentrate the forces tending to rupture the bridge at the point of attachment of each bridge to the band and to the skirt.
The thread on the internal surface of the skirt of the closure is preferably formed of a series of thread segments arranged, starting from a first thread segment distal to the top, along a helical thread locus. Each of the thread segments, except the first, is preferably formed with two substantially planar end surfaces which are inclined to the axis of the closure and face away from the closure top, ie, they face in the direction that a mould core used to mould the closure was withdrawn. The term xe2x80x9csubstantially planar surfacexe2x80x9d is used to mean a surface which is actually planar or which is cured provided that it all faces in the defined direction. The first of the thread segments is preferably pointed at its end distal to its one adjacent thread segment to assist in mating the thread on the closure with a corresponding thread on the neck of a container.
The substantially planar ends of the thread segments are also preferably inclined to a notional radial planes of the closure extending from the longitudinal axis of the closure to the end of the respective thread segment such that the ends are inclined to the cylindrical skirt by an included angle that is less than the included angle that the respective notional radial plane makes with that skirt.
To assist in the venting of gas between the thread segment the spaces between the segment in adjacent turns of the thread are aligned. A groove may be provided on the inside surface of the skirt of the closure extending longitudinally thereof through the aligned spaces.
In another embodiment the present invention consists in an injection moulded article including a cylindrical wall having a thread formed on its radially inner surface, the thread being comprised of a plurality of segments arranged in spaced apart array along the helical locus of the thread, at least some of the thread segments terminating at at least one end in a substantially planar surface inclined to the axis of the thread and facing the direction in which a mould core used in the moulding of the article was withdrawn.
The closure is preferably formed with means for sealingly engaging with the container to prevent leakage therefrom. Any one of the large number of alternative sealing arrangements known may be used with the closure according to the present invention. These include integral sealing ribs or flanges, wadding or flowed-in gaskets.
The sealing arrangement preferably comprises an annular sealing rib which projects downwardly from an underside of the top of the closure, the rib including a first portion having a substantially cylindrical inner surface, the first portion being contiguous with the top and lying adjacent to the skirt of the closure and a second, frusto-conical, portion contiguous with an end of the first portion distal to the top and extending radially inwardly to terminate in a circular free edge, the first portion having an internal diameter at least equal to an external diameter of the neck of the container to which the closure is to be attached such that during threaded engagement of the closure with the neck, the second, frusto-conical, portion will be engaged by a free end of the neck and folded back against the substantially cylindrical inner surface of the first portion of the rib to form a gas-tight seal between at least an outer surface of the neck of the container and the closure.
The closure most preferably has a skirt having a substantially cylindrical form carrying on its outside surface a series of fine vertical ribs terminating at the lower edge of the skirt in a narrow circumferential rib. The frangible bridges are preferably considerably thinner in their radial dimensions than the skirt and the band and the inner surface of the bridges lie flush with the respective radially inner surfaces of the skirt and the band. The radially outer surface of the band is of a slightly smaller diameter than the skirt except in the areas of local thickening which project radially outwardly beyond the radial extent of the skirt.
In this most preferred embodiment of the inside surface of the skirt is preferably generally cylindrical with a helical array of thread segments extending radially inwardly of that surface. The thread segments are separated from one another by axially aligned spaces. The inside of the band is preferably defined by a smooth upper cylindrical surface above the rib of the same diameter as the inside surface of the skirt. The rib is preferably formed of rib segments in axial alignment with the thread segments on the inside surface of the skirt and with the spaces between the rib segments in axial alignment with the spaces between the thread segments. Below the rib the inside surface of the band is inclined downwardly and outwardly so that the band is a little thinner at its lower end than it is at the upper end. This inclined surface carries an array of projections which are axially aligned and of a thickness less than that of the rib segments. Alternate ones of the projections abut at their upper end against the mid point of one of the rib segments, while the other projections are each aligned with one of the spaces between the rib segments.